Topsheets comprised of formed films were designed to be useful in absorptive devices for reducing “rewet.” Rewet may be the tendency for fluids absorbed in the absorbent core to come back onto the skin. Using a formed film topsheet creates a drier surface to the user after fluid insults and have been primarily functional in the feminine napkin use. However, the vast majority of women, about 60% or more, prefer the comfort of a nonwoven topsheet.
While nonwoven topsheets may be more comfortable, especially being worn in non-menstrual days in anticipation of needing protection soon, nonwoven topsheets will wick fluids back to the skin during menstrual days causing rewet, whereas a formed film topsheet generally will not cause rewet. A typical formed film topsheet may occlude the skin with a skin contact area of at least about 27.5%, with some films as high as 62.5%, which may cause a clammy feeling when worn on pre-menstrual days, because the skin occlusion area may not allow the skin's sweat to evaporate to the open atmosphere. The skin may not be able to “breathe” when occluded by a plastic, fluid impermeable region. The skin contact area essentially correlates to what may be called the “land surface area” of a formed film.
It was later discovered that by placing a formed film topsheet in a sublayer position beneath a nonwoven topsheet, the wearer benefited by having some of the comfort of the nonwoven, plus the reduction of rewet. The skin occlusion factor of the formed film was not completely eliminated because the combination also created a zone of residual wetness at the interface between the film's land surface area and the nonwoven laying upon it. Although not ideal, the formed film sublayer, which was used for reducing rewet by having no wicking, created a dryer surface in use, even with the residual wetness that was introduced, as compared to nonwoven topsheet alone or nonwoven topsheet and nonwoven sublayers between the topsheet and the core.
In addition, formed film topsheets used as sublayers served to reduce rewet, but did not distribute the fluids after the insult region had become saturated by multiple insults. This may have been especially recognized in diapers. After at least about 2 to 3 insults (depending on the core's construction and components) the core region in proximity with the insult position becomes saturated. The structure of the formed film topsheets did not provide sufficient void space to let the unabsorbed fluids of the 4th or 5th insults move laterally to be distributed to unused regions of the core.
In order to address this issue, additional formed films known as “acquisition distribution layers” (also known as “ADLs”) emerged useful as sublayers that reduce rewet, but could also distribute fluids to unsaturated regions of the core. ADLs were developed to provide the fluid distribution performance that was lacking by merely laying a formed film topsheet in a sublayer position between a nonwoven topsheet and an absorbent core. Acquisition distribution layers typically have a high void volume and may be designed for rapid acquisition of insult fluids and broader distribution of the fluids to other areas in the absorbent core once the area of the core that is in the insult region has become saturated by previous insults. When the absorbent core area that is in the insult region becomes saturated by multiple insults, volume space is sufficient to allow the fluids to move laterally to unused regions of the core. To date, however, these films remained comprised of, although in a larger scale, a uniform repetitive array of geometrically shaped formed film cells.
A formed film acquisition distribution layer with high void space that may be useful for distribution of insult fluids, but have the repetitive array of geometrically shaped cell depressions, may also have an excessive land surface area that holds residual wetness and occludes the skin as it lies beneath a nonwoven topsheet. A new problem has also been observed with the acquisition distribution layers of the prior art in that the regularly shaped and spaced apart repetitive arrays of cell depressions can cause “skin marking” on a baby's buttocks with overnight use where the baby is lying prone on the diaper. This skin marking, the pressing and temporary maintaining of the pattern in the baby's skin (something like a pillow wrinkle on one's face in the morning), may cause the baby's parent to think the baby has obtained a rash.
In addition, the repetitive array of wells, holes, cells, depressions, or other synonymous terms, can be visible to the parent beneath the nonwoven topsheet. Unfortunately, this negative visual “trigger” of seeing this repetitive array of similar geometric shaped cells may cause some parents to avoid buying the product, even though it is very functional and provides for a healthier skin for their baby. As such, current acquisition distribution layers may not maintain the functions of rapid acquisition and distribution of insult fluids, may not be invisible to the parent, and also may not provide for less residual wetness and skin occlusion land surface area.
These deficiencies in the prior art have lead those skilled in the art to seek further improvements to acquisition distribution layers and absorptive devices incorporating such acquisition distribution layers.